1,653 research outputs found
Gravitational lens candidates in the E-CDFS
We report ten lens candidates in the E-CDFS from the GEMS survey. Nine of the
systems are new detections and only one of the candidates is a known lens
system. For the most promising five systems including the known lens system, we
present results from preliminary lens mass modelling, which tests if the
candidates are plausible lens systems. Photometric redshifts of the candidate
lens galaxies are obtained from the COMBO-17 galaxy catalog. Stellar masses of
the candidate lens galaxies within the Einstein radius are obtained by using
the -band luminosity and the color-based stellar mass-to-light ratios.
As expected, the lensing masses are found to be larger than the stellar masses
of the candidate lens galaxies. These candidates have similar dark matter
fractions as compared to lenses in SLACS and COSMOS. They also roughly follow
the halo mass-stellar mass relation predicted by the subhalo abundance matching
technique. One of the candidate lens galaxies qualifies as a LIRG and may not
be a true lens because the arc-like feature in the system is likely to be an
active region of star formation in the candidate lens galaxy. Amongst the five
best candidates, one is a confirmed lens system, one is a likely lens system,
two are less likely to be lenses and the status of one of the candidates is
ambiguous. Spectroscopic follow-up of these systems is still required to
confirm lensing and/or for more accurate determination of the lens masses and
mass density profiles.Comment: 12 pages, 5 figures, 3 tables, ApJ accepte
Vortices in Ginzburg-Landau billiards
We present an analysis of the Ginzburg-Landau equations for the description
of a two-dimensional superconductor in a bounded domain. Using the properties
of a special integrability point of these equations which allows vortex
solutions, we obtain a closed expression for the energy of the superconductor.
The role of the boundary of the system is to provide a selection mechanism
for the number of vortices.
A geometrical interpretation of these results is presented and they are
applied to the analysis of the magnetization recently measured on small
superconducting disks. Problems related to the interaction and nucleation of
vortices are discussed.Comment: RevTex, 17 pages, 3 eps figure
Correlation functions of eigenvalues of multi-matrix models, and the limit of a time dependent matrix
We consider the correlation functions of eigenvalues of a unidimensional
chain of large random hermitian matrices. An asymptotic expression of the
orthogonal polynomials allows to find new results for the correlations of
eigenvalues of different matrices of the chain. Eventually, we consider the
limit of the infinite chain of matrices, which can be interpreted as a time
dependent one-matrix model, and give the correlation functions of eigenvalues
at different times.Comment: Tex-Harvmac, 27 pages, submitted to Journ. Phys.
On the Resolution of the Time-Like Singularities in Reissner-Nordstrom and Negative-Mass Schwarzschild
Certain time-like singularities are shown to be resolved already in classical
General Relativity once one passes from particle probes to scalar waves. The
time evolution can be defined uniquely and some general conditions for that are
formulated. The Reissner-Nordstrom singularity allows for communication through
the singularity and can be termed "beam splitter" since the transmission
probability of a suitably prepared high energy wave packet is 25%. The high
frequency dependence of the cross section is w^{-4/3}. However, smooth
geometries arbitrarily close to the singular one require a finite amount of
negative energy matter. The negative-mass Schwarzschild has a qualitatively
different resolution interpreted to be fully reflecting. These 4d results are
similar to the 2d black hole and are generalized to an arbitrary dimension d>4.Comment: 47 pages, 5 figures. v2: See end of introduction for an important
note adde
Nucleus-Electron Model for States Changing from a Liquid Metal to a Plasma and the Saha Equation
We extend the quantal hypernetted-chain (QHNC) method, which has been proved
to yield accurate results for liquid metals, to treat a partially ionized
plasma. In a plasma, the electrons change from a quantum to a classical fluid
gradually with increasing temperature; the QHNC method applied to the electron
gas is in fact able to provide the electron-electron correlation at arbitrary
temperature. As an illustrating example of this approach, we investigate how
liquid rubidium becomes a plasma by increasing the temperature from 0 to 30 eV
at a fixed normal ion-density . The electron-ion
radial distribution function (RDF) in liquid Rb has distinct inner-core and
outer-core parts. Even at a temperature of 1 eV, this clear distinction remains
as a characteristic of a liquid metal. At a temperature of 3 eV, this
distinction disappears, and rubidium becomes a plasma with the ionization 1.21.
The temperature variations of bound levels in each ion and the average
ionization are calculated in Rb plasmas at the same time. Using the
density-functional theory, we also derive the Saha equation applicable even to
a high-density plasma at low temperatures. The QHNC method provides a procedure
to solve this Saha equation with ease by using a recursive formula; the charge
population of differently ionized species are obtained in Rb plasmas at several
temperatures. In this way, it is shown that, with the atomic number as the only
input, the QHNC method produces the average ionization, the electron-ion and
ion-ion RDF's, and the charge population which are consistent with the atomic
structure of each ion for a partially ionized plasma.Comment: 28 pages(TeX) and 11 figures (PS
The Effect of Cataract on Color Vision Measurement with the Low-Vision Cambridge Colour Test
Purpose:
To quantify the effect of cataract on colour vision as measured by the low vision Cambridge Colour Test (lvCCT). A secondary aim of our study was to understand whether different types and severities of cataract have different effects on colour vision.
Design:
Cohort study
Subjects:
Patients aged 18 - 95 years attending for routine cataract surgery at the Oxford Eye Hospital.
Methods:
The lvCCT was performed to measure colour sensitivity in both eyes in a cohort of patients undergoing routine cataract surgery both pre-operatively and post-operatively. The crystalline lens was examined and graded according to the Lens Opacities Classification System III (LOCS III) to determine the type and severity of cataract. Measures of repeatability were performed for the data to explore test-retest bias using Bland-Altman analysis. The Wilcoxon signed-rank test was performed to assess the effect of cataract on colour vision by comparing control and surgical test measurements. Three multiple linear regressions were performed to relate cataract grading or severity to colour vision measurements.
Main outcome measures:
Colour discrimination along each of the protan, deutan, and tritan confusion lines.
Results:
The Wilcoxon signed-rank test showed a statistically significant difference in both the protan (P=0.024) and tritan (P=0.020) axes upon comparison of control and surgical test measurements. As severity of cataract increased colour vision sensitivity was more greatly affected, and nuclear sclerotic cataract had the most profound effect upon colour vision sensitivity in the lvCCT. The linear regression models though showed these observations did not reach statistical significance.
Conclusions:
Cataract surgery has a statistically significant effect upon colour vision in both the protan and tritan axes. The effects of specific subtypes of cataract and different severities could not be elucidated due to the high prevalence of patients presenting with mixed cataract. LvCCT colour sensitivity measurements are regularly used as outcome measures in clinical gene therapy trials involving vitreoretinal surgery, and vitrectomy accelerates cataract formation. Therefore, it is important to quantify the effect of cataract upon colour vision measurements so it may be taken into account when used as an outcome measure in clinical trials. We were unable to derive a precise correction factor for cataract on color vision measurements
A New Window of Exploration in the Mass Spectrum: Strong Lensing by Galaxy Groups in the SL2S
The existence of strong lensing systems with Einstein radii (Re) covering the
full mass spectrum, from ~1-2" (produced by galaxy scale dark matter haloes) to
>10" (produced by galaxy cluster scale haloes) have long been predicted. Many
lenses with Re around 1-2" and above 10" have been reported but very few in
between. In this article, we present a sample of 13 strong lensing systems with
Re in the range 3"- 8", i.e. systems produced by galaxy group scale dark matter
haloes, spanning a redshift range from 0.3 to 0.8. This opens a new window of
exploration in the mass spectrum, around 10^{13}- 10^{14} M_{sun}, which is a
crucial range for understanding the transition between galaxies and galaxy
clusters. Our analysis is based on multi-colour CFHTLS images complemented with
HST imaging and ground based spectroscopy. Large scale properties are derived
from both the light distribution of the elliptical galaxies group members and
weak lensing of the faint background galaxy population. On small scales, the
strong lensing analysis yields Einstein radii between 2.5" and 8". On larger
scales, the strong lenses coincide with the peak of the light distribution,
suggesting that mass is traced by light. Most of the luminosity maps have
complicated shapes, indicating that these intermediate mass structures are
dynamically young. Fitting the reduced shear with a Singular Isothermal Sphere,
we find sigma ~ 500 km/s and an upper limit of ~900 km/s for the whole sample.
The mass to light ratio for the sample is found to be M/L_i ~ 250 (solar units,
corrected for evolution), with an upper limit of 500. This can be compared to
mass to light ratios of small groups (with sigma ~ 300 km/s and galaxy clusters
with sigma > 1000 km/s, thus bridging the gap between these mass scales.Comment: A&A Accepted. Draft with Appendix images can be found at
http://www.dark-cosmology.dk/~marceau/groups_sl2s.pd
Morphology of supported polymer electrolyte ultra-thin films: a numerical study
Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM
fuel cell catalyst layers has significant impact on the electrochemical
activity and transport phenomena that determine cell performance. In those
regions, Nafion can be found as an ultra-thin film, coating the catalyst and
the catalyst support surfaces. The impact of the hydrophilic/hydrophobic
character of these surfaces on the structural formation of the films has not
been sufficiently explored yet. Here, we report about Molecular Dynamics
simulation investigation of the substrate effects on the ionomer ultra-thin
film morphology at different hydration levels. We use a mean-field-like model
we introduced in previous publications for the interaction of the hydrated
Nafion ionomer with a substrate, characterized by a tunable degree of
hydrophilicity. We show that the affinity of the substrate with water plays a
crucial role in the molecular rearrangement of the ionomer film, resulting in
completely different morphologies. Detailed structural description in different
regions of the film shows evidences of strongly heterogeneous behavior. A
qualitative discussion of the implications of our observations on the PEMFC
catalyst layer performance is finally proposed
On Second-Order Monadic Monoidal and Groupoidal Quantifiers
We study logics defined in terms of second-order monadic monoidal and
groupoidal quantifiers. These are generalized quantifiers defined by monoid and
groupoid word-problems, equivalently, by regular and context-free languages. We
give a computational classification of the expressive power of these logics
over strings with varying built-in predicates. In particular, we show that
ATIME(n) can be logically characterized in terms of second-order monadic
monoidal quantifiers
The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of
the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of
scientists from Japan, Taiwan and Princeton University is using HSC to carry
out a 300-night multi-band imaging survey of the high-latitude sky. The survey
includes three layers: the Wide layer will cover 1400 deg in five broad
bands (), with a point-source depth of . The
Deep layer covers a total of 26~deg in four fields, going roughly a
magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter
still in two pointings of HSC (a total of 3.5 deg). Here we describe the
instrument, the science goals of the survey, and the survey strategy and data
processing. This paper serves as an introduction to a special issue of the
Publications of the Astronomical Society of Japan, which includes a large
number of technical and scientific papers describing results from the early
phases of this survey.Comment: 14 pages, 7 figures, 5 tables. Corrected for a typo in the
coordinates of HSC-Wide spring equatorial field in Table
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